Importing .mov files in blender sequencer is very laggy
Importing .mov is not the issue. Mov files are quicktime files. Quicktime is a container that can hold video files in a variety of different compression codecs. Some codecs are more efficient than others. Some codecs require more from the CPU than others. Some require faster drives to sustain the data rate. Some are fast and easy to play at the expense of quality. All quicktime files are not created equal.

The same can be said about mvk. It is a container, that can encode in different codecs. Some will work for you, others won't. Sustaining the data rate depends depends on the codec and the resources available on your computer.

But the bottom line is that editing 4k video requires a lot of computing power, and/or clever optimization. Blender's video editing capabilities are quite limited and antiquated. To deal with video you would be better off with a real video editing app. Most of them can play video more efficiently than blender, using GPU acceleration and multithreaded operations. Blender uses none of that.

Blender is a great 3D app but the vse's performance and design is sub-par to other apps out there in the real world.